Brake Caliper Pistons

C

Cambo

Active member
Hey Barfers!

I am rebuilding the front calipers on my sv, has a K5 1000 front end so it's the four pot Tokico's.

I don't have a compressor yet, so I used grips with padding to remove the pistons and you guessed it! I nicked the exterior of two pistons. No bad at all but you can sure feel that tiny sharp edge when the rest of the surface is so smooth.

Question:
Can I use various grades of wet and dry to take the edges off of the pistons where it is nicked and polish them back up, or do I need to replace them?

Thanks in advance.
D.
 
295566

295566

Numbers McGee
I'd replace.. your brakes aren't something you want to do a half-assed repair job on. :)
 
Shigeta

Shigeta

Moving Chicane
It's likely that you'll need to replace the pistons. As I'm sure you already know, the sharp edge can tear the seal or allow fluid or debris to pass through.

Going through the process of sanding/polishing will take quite a long time. Even if you get it perfectly smooth again, I'd imagine there is quite a high likelihood that the process will take enough material off to create a less-than-ideal seal.

I'd bet you can find new pistons for the price of all of the sandpaper it'd take to attempt to work out the nicks.

If I don't have compressed air when I'm removing calipers, I usually reach for this tool. It grabs the piston well on the inside instead of the outside.
 
ST Guy

ST Guy

Well-known member
Replace.

Next time get a C clamp and pad both sides.

OK....never mind. I was thinking of squeezing them in instead of removing them.
 
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OaklandF4i

OaklandF4i

Darwin's exception
Replace is the best solution.

If you got real lucky and the nick is only present on the very end of the piston that doesnt retract into the seal with new pads installed, you might get away with reusing as it wont affect the seal. Most likely that isnt the case as most pistons fully retract with new pads.

Dont bother trying to sand it out. Just replace.

FYI, I keep pads made from old rubber inner tubes to protect parts I need to grab in my vice or with other tools.

If you dont have a compressor, you can use the brake lever to pump them out, will need to add a significant amount of fluid to the reservoir as you do it. If they dont pop out the the first time, clean the exposed portion, smear with oil, and push back in. Repeat process until they pop out. Pro process is air compressor however.
 
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ST Guy

ST Guy

Well-known member
GPzPop said:
Pro-Tip : keep your fingers out of the gap when you do this!

DAMHIK-IJK,OK
Click to expand...

Yep. And it's also best to make sure there's something to stop the from flying out and getting damaged. Depending upon the calipers, you can simply slip a piece of wood between the pistons and the other side of the caliper. Or aim the pistons into a box filled with old rags and stuff to cushion them when the fly out.
 
afm199

afm199

Well-known member
OaklandF4i said:
Replace is the best solution.

If you got real lucky and the nick is only present on the very end of the piston that doesnt retract into the seal with new pads installed, you might get away with reusing as it wont affect the seal. Most likely that isnt the case as most pistons fully retract with new pads.

Dont bother trying to sand it out. Just replace.

FYI, I keep pads made from old rubber inner tubes to protect parts I need to grab in my vice or with other tools.

If you dont have a compressor, you can use the brake lever to pump them out, will need to add a significant amount of fluid to the reservoir as you do it. If they dont pop out the the first time, clean the exposed portion, smear with oil, and push back in. Repeat process until they pop out. Pro process is air compressor however.
Click to expand...

This. If the nick never hits the seal it doesn't matter. That's at least a quarter inch or more of distance.
 
ST Guy

ST Guy

Well-known member
Nasty. Replace.

Even if you could smooth out the high spots, you'd still have negative spaces with surrounding sharp edges.
 
C

Cambo

Active member
Entire caliper was $32 so I went that route, thank you for the information and opinions. I will take a different approach when removing the pistons on the next one.

Cheers!
 
kuksul08

kuksul08

Suh Dude
You can measure the distance from teh edge of the piston to the furthest nick, and then from the edge of the caliper to the pressure seal (second one). If the nicks are above the seal you're fine.
 
Busy Little Shop

Busy Little Shop

Man behaving bikely...
Non destructive steps to remove caliper pistons...

1) remove pads and flush out brake dust with Acetone...
2) pump master cylinder to move pistons equally to the center of the caliper...
3) start cleaning exposed pistons with a micro fine pads dipped in Acetone...
4) finish cleaning pistons with rag wet with Acetone...
5) lube pistons with appropriate brake lube...
6) finally with the pistons cleaned and lubed they should move freely wrapped in a rag with just the power of your hands...
 
afm199

afm199

Well-known member
Good advice in this thread.

Re the picture. If there were ONE of those dings, the one closest to the face that pushes the pad, I might buff the sharp edges off and use it. But that many, no.
 
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